Plate antenna with protective cover

ABSTRACT

A plate antenna as used, for example, in combination with a proximity door operator system has a capacitive signal plate situated between two shielding panels of fiber glass and cemented to such panels to form a unitary structure which, in turn, is placed below floor level so that anyone passing thereover increases the relative capacitive coupling necessary for related door actuation.

United States Patent 91 Schultz PLATE ANTENNA WITH PROTECTIVE COVER [76] Inventor: Frederick C. Schultz, 15448 Rudland, Roseville, Mich. 48066 [22] Filed: July 17, 1972 21 Appl. No.: 272,337

[52] US. Cl. 343/873, 343/897 [51] Int. Cl. H0lq 1/40 [58] Field of Search 343/872, 873, 897

[56] References Cited UNITED STATES PATENTS 2,673,931 3/1954 Stevens 343/873 2,750,321 6/1956 Koppelman 343/873 3,633,206 l/l972 McMillan 343/872 DOOR OPERATOR MECHANISM I 1 Jan. 29, 1974 3/1970 Velez 343/873 3,501,767 3,710,337 3/1973 Grant 343/872 2,624,004 12/1952 Polydoroff 343/873 Primary Examiner-Eli Lieberman Attorney, Agent, or Firm-Lon H. Romanski ABSTRACT 3 Claims, 3 Drawing Figures RECEPJER TRANSMITTER J. PLATE ANTENNA RECEIVER ANTENNA n TRANSMITTER PLATE. DRIVER TRANSMITTER Pmmnumw 3.789.419

DOOR OPERATOR MECHANISM /Z RECEIVER AMPLIFIER RELAY DETECTOR DRIVER TRANSMITTER w /5 PLATE DRIVER 'OSCILLATO R I PLATE ANTENNA-J SYNC RONOUS PLATE ANTENNA WITII PROTECTIVE COVER BACKGROUND OF THE INVENTION Heretofore various devices have been proposed by the prior art for automatically sensing the presence of, for example, a person in proximity to a door and in response thereto automatically opening such door to enable the free passage through the related doorway.

One of such devices employs, among other things, a transmitter plate antenna assembly imbedded within the floor or walk-way and a receiver antenna situated above and in spaced relationship to the transmitter plate antenna.

In the prior art, such transmitter plate antennas were usually constructed of an antenna plate (whether a solid sheet of metal or of screen-like configuration) with shielding-like panels or plates situated on opposite sides of the antenna plate. Such three combined elements were then placed within a chamber or recess below floor or walk-way level and then encapsulated with, for example, epoxy. However, such prior art shielding-like panels were formed of plastisol materials. It was found that such prior art assemblies had a relatively short useful life in that cracks and other similar failures would soon occur in the epoxy of encapsulating material and such failures would rapidly increase in severity thereby causing an overall failure requiring the removal and replacement of the transmitter plate antenna assembly.

It is believed that such structural failures and resulting functional failures were caused by the compressibility of the plastisol materials. That is, because such materials do exhibit a degree of resilience, whenever the epoxy immediately above and below the plate antenna assembly was subjected to a load, as by persons stepping on it, the encapsulated plastisol materials would undergo compressive deformation thereby requiring corres-ponding deflection of the relatively brittle epoxy immediately above. This in turn caused progressive cracking of the encapsulating epoxy and ultimately failure of the entire assembly.

- Accordingly, the invention has herein disclosed and described is directed primarily to the solution of the above as well as other related problems.

SUMMARY OF THE INVENTION According to the invention, a plate antenna assembly comprises a first upper disposed shielding-like panel, a second lower disposed shielding-like panel, and an intermediate electrically conductive plate-like antenna, said first upper panel being adhesively bonded to an upper side of said plate-like antenna, and said second lower panel being adhesively bonded to a lower side of said plate-like antenna.

Various general and specific objects and advantages of the invention will become apparent when reference is made to the following written description of the invention considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, where for purposes of clarity certain details and elements may be omitted from one or more views:

FIG. 1 shows a perspective view, partly in section, of an illustrative door operator system (including a representative block diagram of related electronic components) employing a transmitter plate entenna assembly constructed in accordance with the teachings of this invention;

FIG. 2 is an enlarged cross-sectional view taken generally on the plane of line 2-2 of FIG. 1 and looking in the direction of the arrows; and

FIG. 3 is a simplified perspective view of a possible configuration of one of the elements shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in greater detail to the drawings, FIG. 1 illustrates an embodiment of a power operated door embodying the present invention. In the illustrated embodiment, a power operated door 10, shown as being a swinging door, is provided with a suitable power operator mechanism 12 for opening and closing the door automatically in response to the traffic therethrough.

The door 10 is provided with a transmitter plate antenna 14 at the approach to the doorway which cooperates with a receiver antenna 16 mounted above the doorway to produce a signal to initiate the automatic operation of the door 10. It should, of course, be understood that a second transmitter plate antenna and a second receiver antenna (neither of which is shown for simplicity of illustration) may be positioned on the other side of the door to produce a signal in response to traffic approaching from the opposite direction.

A control box 17, which may be located remotely from the doorway, houses an oscillator 18, a transmitter plate or antenna driver 20, a synchronous detector 22 and a relay driver 24 generally connected as shown.

The above system, which forms no part of this invention, operates generally as follows. The oscillator 18 produces a particular output frequency, of preselected value, for driving a transmitter plate for actuating the automatic control system. The said preselected output frequency is connected to a first input of the synchronous detector 22 and to the input of transmitter plate driver 20.

The receiver antenna 16 is coupled to the amplifier 19 the output of which is, in turn, coupled to a second input of the synchronous detector 22 which, as previously stated, also receives the said preselected output frequency. The synchronous detector 22 contains a integrating capacitor that is constantly being charged and bled off. The strength of the signal supplied to the transmitter plate driver 20 is such so that when no conductive object is present between the antenna plates, the capacitor charge never reaches a sufficient level to trigger the relay driver 24. When such an object is present, however, the capacitive coupling between the an tenna plates increases and this causes a corresponding increase in the output of the receiver amplifier 19. The increased receiver amplifier 19 output then charges the capacitor to a level which energizes the relay driver 24 which, in turn, actuates the door operator mechanism 12 to open the door 10. When the conductive object leaves the area, the output of amplifier 19 diminishes to its steady state level; the relay driver 24 is deenergized and the door 10 closes.

The invention as herein described and disclosed is primarily concerned with the transmitter plate antenna assembly 14 as used within a system as disclosed above and more particularly to an improved construction of such transmitter plate antenna assembly as well as its placement within the walk area.

FIG. 2, a cross-sectional view taken generally on the plane of line 2-2 of FIG. 1 and looking in the direction of the arrows, for purposes of clarity, illustrates the various elements out of scale and out of relative proportion. Nevertheless, as generally shown in FIG. 1, a walkway 30, formed as of concrete, has a chamber or recess 32 formed therein for the reception of the plate antenna assembly 14.

In the preferred embodiment, the plate antenna assembly is comprised of upper and lower disposed sections of glass-fiber reinforced polyester plastic panels 34 and 36, respectively, between which is contained an electrically conductive or charge carrying member 38 which, in the preferred embodiment is a sheet of aluminum. The upper and lower fiber glass sheets or sections 34 and 36 are preferably rectangular or square in outer configuration as is the electrically conductive plate 38.

The plate antenna assembly 14 is formed by applying a bonding cement or adhesive to the upper surface of the lower fiber glass section 36 and to the lower surface of the upper fiber glass section 34 and, by means of such adhesive, bonding the electrical plate 38 to both sections of fiber glass. Preferably such stacked elements (the two fiber glass sections or panels and the sandwiched electrical plate 38) are pressed together as by the application of an external force in order to enhance bonding and flatness of the assembly 14. The related conductor means 40, leading to the control means 17, may, of course, be connected to the plate 38 in any suitable manner as, for example, soldering.

In at least one successful embodiment of the preferred form of the invention, the thickness of the upper fiber panel 34, as depicted by dimension A, was in order of 0.035 inches, while the lower fiber glass panel 36, as represented by dimension C, was in the order of 0.040 inches thick. In this same embodiment, the conductive plate 38 was of aluminum and in the order of 0.003 inches thick, as depicted by dimension B. Each of such elements were purchased as commerically available material with the usual associated commerical dimensional tolerances.

Further, even though many sources are available for the purchase of acceptable materials for the practice of the invention, the following have been found to be particularly suitable. For example, the upper fiber glass panel 34 was a standard product sold by FILON a Division of VISTRON CORP. and identified in a FILON catalog (copyright 1971 by Vistron Corp.) as being: 4.0 oz. fiber glass sheet with a dielectric constant of 3.7 and having a thickness of 0.035 inches. The lower fiber glass panel 36 was a standard product also sold by the same FILON, Division of Vistron Corp., and identified in the same catalog referred to above as being: 5.0 oz. fiber glass sheet with a dielectric constant of 3.6 and having a thickness of 0.040 inches.

Another source for such plastic panel sheets is Barcley Industries. Such fiber glass material, identified in 1971 product advertising literature of Barcley Industries, identified the particular grade as being type 600." Again, in the preferred embodiment, the upper plate 34 would be of 4.0 oz. weight having a dielectric constant in the order of 3.7 and a thickness of 0.035 inches while the lower panel 36 would be of 5.0 oz. weight having a dielectric constant in the order of 3.6 and a thickness of 0.040 inches.

Although various contact type cements or adhesives are suitable to the practice of the invention, including any of the polyester resins, it has been found that the following and their equivalents are preferred. The'first of such contact elements is identified as: No. 2210 pro duced and sold by the 3M Company of St. Paul, Minnesota. Such No. 2210 contact cement (having a polychloroprene base) is identified on 3M Company product specification sheet dated Oct. 1, 1966, and meets the specification requirements of Federal Government Military specifications identified as: MIL-A-l 154C; MIL-A-2l366 and MMM-A-00130. A second of such contact cements is identified as: No. 1357 produced and sold by the 3M Company. Such No. 1357 contact cement is identified on the 3M Company product specification sheet dated Oct. 1, 1966, and meets the specification requirements-of Federal Government Military specifications identified as: MIL-A-1l54C and MIL- A-21366. A third of such contact cements is identified as: No. 2218 produced and sold by the 3M Company. Such No. 2218 contact cement is identified on the 3M Company product specification sheet dated Oct. 1, 1966, and meets the specification requirements of Federal Government Military specifications identified as: MIL-A-1154C.

After the antenna plate assembly 14 is constructed, it is placed within the chamber or recess 32 and there surrounded by a filler 42 which includes, as an ingredient, epoxy cement. Preferably, the top surface 44 of the filler 42 is made as to be flush with the surrounding walk-way surface 46 with such surfaces 44 and 46 defining a floor surface.

In the preferred form, the filler 42 is comprised of a mixture of epoxy (in the order of 2.0 parts by weight) a hardener (in the order of 1.0 part by weight) and sand (in the order of 6.0 to 7.0 parts by weight). Although various brands of epoxy are suitable, it has been found that the following brands are particularly suited. That is, GENEPOXY Brand No. M-l manufactured and sold by General Mills Co. and identified in its product bulletin No. A-24-044 as well as GENAMID Brand hardener also manufactured and sold by General Mills Co. and identified in its product bulletin No. ll-D-3A (Rev. 9-65) have provided desirable results in at least one successful embodiment.

Further, in the preferred form, the sand constituent is comprised of Ottowa silica sand of 40-80 mesh grain size. Such has what is generally referred to as rounded edges thereby enhancing the structural integrity of the filler when hardened.

Referring specifically to FIG. 2, in the preferred form, the chamber 32 and the assembly 14 are preferably of such dimensions and configurations as to result in dimension D, the distance between the lower fiber glass panel or plate 36 and the bottom surface 48 of chamber 32, being in the order of of A to V4 inches and dimension E, the distance between the top surface of the upper fiber glass panel or plate 34 and the upper surface 44 of the filler 42, being in the order of )4 inches.

Along with the other benefits derived, the various elements comprising the invention exhibit coefficients of thermal expansion approximately equal to each other thereby minimizing any possible damage arising from thermal stresses especially when one considers the rather limited dimensions involved.

The resulting structure, as depicted in FIG. 2, has been found to be greatly superior to the prior art structures and, even though exposed to heavy traffic conditions and the total spectrum of weather conditions, has not shown any evidence of any structural failure or functional deterioration.

Although only the preferred embodiment of the invention has been disclosed and described, it is apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims. For example, instead of the upper and lower panels 34 and 36 being of fiber glass, it has been discovered that such could be formed of urethane or sheets of epoxy laminations; also, the inner member 38 need not be a continuous sheet of metallic or other electrically conductive material but may in fact be formed as a screen-like member as depicted at 50 of FIG. 3.

I claim:

1. A plate antenna assembly for use as a signal plate of a capacitance sensitive door operator for detecting a capacitance change caused by traffic thereabove, comprising a first upper disposed fiber glass shieldinglike panel, a second lower disposed fiber glass shielding-like panel, and an intermediate electrically conductive plate-like antenna, said first upper panel being adhesively bonded to an upper side of said plate-like antenna, and said second lower panel being adhesively bonded to a lower side of said plate-like antenna, said upper and lower panels being of such dimensions as to extend peripherally beyond the peripheral edge of said plate-like antenna, said upper fiber glass panel having a cross-sectional thickness in the order of 0.035 inches, and said lower fiber glass panel having a cross-sectional thickness in the order of 0.040 inches.

2. A plate antenna assembly according to claim 1 wherein said intermediate electrically conductive plate-like mamber has a screen-like configuration.

3. A plate antenna assembly according to claim 1 wherein said upper and lower shielding-like panels and said intermediate plate-like antenna are encapsulated within encapsulating material comprising epoxy and silica sand, said silica sand comprising Ottowa silica sand of 40-80 mesh grain size, and said encapsulating material being effective to encapsulate said panels and said plate-like antenna and to secure said panels and said plate-like anntena to an associated receiving chamber. 

1. A plate antenna assembly for use as a signal plate of a capacitance sensitive door operator for detecting a capacitance change caused by traffic thereabove, comprising a first upper disposed fiber glass shielding-like panel, a second lower disposed fiber glass shielding-like panel, and an intermediate electrically conductive plate-like antenna, said first upper panel being adhesively bonded to an upper side of said plate-like antenna, and said second lower panel being adhesively bonded to a lOwer side of said plate-like antenna, said upper and lower panels being of such dimensions as to extend peripherally beyond the peripheral edge of said plate-like antenna, said upper fiber glass panel having a cross-sectional thickness in the order of 0.035 inches, and said lower fiber glass panel having a crosssectional thickness in the order of 0.040 inches.
 2. A plate antenna assembly according to claim 1 wherein said intermediate electrically conductive plate-like mamber has a screen-like configuration.
 3. A plate antenna assembly according to claim 1 wherein said upper and lower shielding-like panels and said intermediate plate-like antenna are encapsulated within encapsulating material comprising epoxy and silica sand, said silica sand comprising ''''Ottowa'''' silica sand of 40-80 mesh grain size, and said encapsulating material being effective to encapsulate said panels and said plate-like antenna and to secure said panels and said plate-like anntena to an associated receiving chamber. 